When milling to create a lateral exit from a tubular string a typical bottom hole assembly will have a measurement while drilling (MWD) sub for guidance of the bottom hole assembly. This device requires flow through it to operate. Additionally an anchor is located below a whipstock above which a milling assembly is located for milling laterally through a tubular wall for an exit for a lateral. The anchor requires a pressure buildup to set. The MWD device assists with orientation of the whipstock ramp in the desired direction before the anchor is set. Typically a ported sub has been used to allow circulation for the operation of the MWD until the desired depth and whipstock orientation is obtained. At that point pressure through a restrictor is built up to break a shear pin holding a movable sleeve. A biasing spring then shifts the sleeve to close the lateral ports in the ported sub with the surface pumping equipment preferably in the off position after the shear pin is severed. Thereafter the pressure is again applied to set the whipstock anchor. After the whipstock anchor is set the pressure is built up to break a rupture disc on the assembly of mills so that flow can go through mill nozzles as the mills are advanced down the whipstock ramp to make the lateral exit or window. Setting the anchor requires no flow but the subsequent operation of flowing through the mills does require flow. The flow in the past design had to go through the restriction orifice used to shift the sleeve from the circulation to the flow through position. This meant that the flow for the milling operation would try to move the sleeve back to the circulation position against the force of the spring that pushed the sleeve in the first place from the circulation to the flow through position. As a result the prior design employed a snap ring to prevent return movement of the sleeve against the force of the bias from the spring. The use of the snap ring to retain the sleeve position proved problematic from several respects. The design was expensive to build and assembly and the snap ring at times hung up and failed to hold the shifted sleeve in position. Another operational problem was the need for the high circulation rates when milling to remove cuttings also mean high pressure drops as the high flow rates required would still have to go through a restriction. The restriction upstream of the mill nozzles also took away a signal to surface personnel as to the flow conditions at the mill nozzles. Finally the use of high flow rates through the restriction created issues of erosion at the restriction and at other locations that saw high velocities. While one design offered by Baker Hughes Incorporated of Houston Tex. accomplished sleeve shifting with pressure buildup that broke a shear pin a competing design used a restriction in conjunction with a j-slot mechanism to reposition a sleeve in the ported sub from a circulation position to a flow through orientation after a predetermined number of cycles of applied and removed pressure. This design also had flow continuing to go through the restriction that enabled the j-slot mechanism after the sleeve was shifted from the circulation to the flow through positions.
FIGS. 1-3 illustrate the basics of the Baker Hughes Incorporated Whipstock Valve described above. A spring 21 pushed on a sleeve 18 when applied pressure broke shear pin 17. In the FIG. 2 position, flow from passage 30 is directed to lateral port 32 for circulation to let the MWD operate. Seals 13 and 15 close off passage 30 to straight through flow. A snap ring 9 moves left past sleeve 8 so that reverse movement of seals 16 cannot happen. Comparing FIGS. 2 and 3 it can be seen that when seal 16 crosses ports 32 it closes off those ports. Coincidentally, movement of sleeve 18 opens passage 30 to allow straight through pressure application to set an anchor for the whipstock and subsequent flow after breaking a rupture disc that previously isolated the mills to allow setting the anchor, to feed the mill nozzles for debris removal as the window is milled. In both FIGS. 2 and 3 the flow goes through the carbide nozzle 7. As can be seen with flow going straight through the valve assembly the flow through the nozzle 7 tries to push the sleeve 18 against the spring 21 so that the snap ring 9 is needed to resist that force. Again the shortcomings of this design were discussed in detail above. The competing design using the j-slot to shift the sleeve position still had similar issues.
The present invention is a redesign of the valve of FIGS. 1-3 with the principal difference being that the restriction is bypassed when the sleeve is shifted by the spring to the flow through position. While there is still some flow through the orifice, the bulk of the flow goes through the bypass so that the biasing spring can hold the sleeve in position for flow through the ported sub even when high flow rates for milling the window are developed. These and other aspects of the present invention will be more readily apparent from a review of the detailed description of the preferred embodiment and the associated drawings while recognizing that the full scope of the invention is to be determined by the appended claims.